An apparatus for a steam engine is known in the art, for example as disclosed in Japanese Patent Publication No. S58-057014, in which working fluid is filled in a fluid container, the working fluid is heated and vaporized by a heating device, and the working fluid is cooled down and liquefied by a cooling device, and in which energy is obtained by repeating vaporization and liquefaction of the working fluid.
Namely, a mechanical energy is obtained in the above steam engine at an output device, which is operated by pressure change of the working fluid in the fluid container, wherein the pressure change is generated by change of state (vaporization and liquefaction) of the working fluid.
The inventors of the present invention have applied for another patent relating to a steam engine in Japanese Patent Office, which is published as a publication number of 2004-84523.
A structure of the steam engine 500 of the prior patent application is shown in FIG. 24.
The steam engine 500 comprises a U-shaped fluid container 502 in which working fluid is filled, a heating device 504 for heating the working fluid in the fluid container 502, a cooling device 506 for cooling down and liquefying steam generated by the heat at the heating device 504, and an output device 508.
The output device 508 comprises a cylinder 510, a piston 512 reciprocating in the cylinder 510, a moving shaft 514 connected at its one end with the piston 512, and a spring 516 connected to the other end of the moving shaft 514, wherein the piston 512 is reciprocated in the cylinder 510 by receiving fluid pressure of the working fluid in the fluid container 502.
In the above steam engine 500, a volumetric expansion of the working fluid (steam) is generated, when the working fluid in the fluid container 502 is heated and vaporized by the heating device 504. The generated steam moves downwardly in the container 502 and is cooled down and liquefied by the cooling device 506. Then, the volume of the working fluid in the fluid container 502 is contracted. The piston 512 and the moving shaft 514 of the output device 508 receive the pressure change generated in the fluid container 502 due to the volumetric expansion and contraction of the working fluid, and thereby the piston 512 is reciprocated.
When a permanent magnet is provided to the moving shaft 514 and an electromagnetic coil is arranged to face to the magnet, an electromotive force is generated in the coil in accordance with the reciprocal movement of the piston 512 and the moving shaft 514, and an electric power is generated.
The above steam engine has, however, some disadvantages or problems as described below:
(1) At first, output energy of the steam engine would become smaller, when a cross sectional area of a cooling portion of the fluid container, at which the steam of the working fluid is liquefied, is not properly designed.
For example, in the case that a cross sectional area of the cooling portion of the fluid container (at which the cooling device is provided) is made extremely small, a heat transfer time for transferring the heat in a cross sectional direction, from an inner surface of the cooling portion to a center of the working fluid in the fluid container, becomes shorter. As a result, a cooling efficiency for the working fluid at the cooling portion becomes higher, so that gas-phase working fluid (the steam) is liquefied within a very short time.
In such a steam engine, the steam generated at the heating device moves toward the cooling device, and the steam is liquefied at once at the cooling portion. A volumetric expansion of the working fluid is suppressed to a small amount, to reduce the output energy at the steam engine. A p-v diagram of the above case is shown in FIG. 23B, wherein a relation between the pressure and volume of the working fluid is indicated by a solid line.
FIG. 23A shows a p-v diagram in the case that the vaporization and liquefaction of the working fluid is properly performed, and the desired value of FIG. 23A is indicated by a dotted line in FIGS. 23B and 23C. As shown in FIG. 23B, an area of the p-v diagram becomes smaller than that of the desired value, and the output energy is correspondingly decreased.
On the other hand, in the case that a cross sectional area of the cooling portion of the fluid container is made extremely large, the heat transfer time for transferring the heat from the inner surface of the cooling portion to the center of the working fluid, becomes longer. As a result, the cooling efficiency for the working fluid at the cooling portion is decreased, so that a longer timer is necessary for liquefying the gas-phase working fluid (the steam).
In such a case, even when the steam generated by the heating device moves to the cooling device, the gas-phase working fluid is maintained for a longer period and the fluid pressure in the fluid container remains at a high value, due to the longer period for the liquefaction. As a result, an area of the p-v diagram becomes smaller, as shown in FIG. 23C, to likewise decrease the output energy. Furthermore, when the gas-phase working fluid remains at the heating device, the liquid-phase working fluid can be hardly vaporized. As a result, the fluid pressure by the vaporization can not be increased, and thereby the operation of the steam engine may be irregularly stopped.
Furthermore, in the case that a cross sectional area of a connecting passage portion of the fluid container (which is a passage portion between the heating device and the cooling device) is made small, the heat transfer time for transferring the heat in a cross sectional direction, from the inner surface of the connecting passage portion to the center of the working fluid in the fluid container, becomes shorter. As a result, the cooling efficiency for the working fluid at the connecting passage portion becomes higher.
In such a case, the steam generated at the heating device is liquefied at the connecting passage portion, when the steam is moved toward the cooling device. A volumetric expansion of the working fluid by the vaporization is suppressed to a small amount, to reduce the output energy at the steam engine, as shown by the p-v diagram of FIG. 23B.
(2) It is necessary not only to increase input energy to the steam engine but also to increase amount of heat exchange to be transferred from the heating and cooling devices to the working fluid, in order to increase the output mechanical energy to be generated at the steam engine. It can be possible to increase the amount of the heat exchange, for example, by setting a temperature of the heating device at a higher value and by setting a temperature of the cooling device at a lower value.
It is, however, inevitably necessary, in the above method of increasing the temperature at the heating device and decreasing the temperature of the cooling device, to increase the input energy to the heating and cooling devices. The output mechanical energy obtained by the steam engine is thereby increased on one hand, but energy loss would be adversely become larger on the other hand, if energy transfer effectiveness from the heat energy to the mechanical energy is low.
The mechanical energy to be generated at the steam engine can be increased by increasing surface areas of a heating and a cooling portion of the fluid container at the respective heating and cooing devices, without changing (increasing or decreasing) preset temperatures of the heating and cooling devices.
In the case that cross sectional areas of the heating and cooling portions of the devices are simply enlarged to increase the surface areas, the heat transfer time in the cross sectional direction of the fluid container, from the inner surface to the center of the working fluid, becomes longer. The heating efficiency and cooling efficiency at the respective heating and cooling portions are thereby decreased, so that the energy transfer effectiveness can not be sufficiently improved. As a result, the mechanical energy can not be sufficiently generated at the steam engine.
(3) In the steam engine 500 shown in FIG. 24, the heating device 504 is so formed to surround the heating portion of the fluid container 502, so that it heats the working fluid in the fluid container 502 from its outer periphery. It is, however, a problem in such steam engine that the heating efficiency is not sufficiently high.
In the heating device 504 as above, namely in which the working fluid is heated from the outer periphery of the fluid container 502, there is a temperature gradient, as shown in FIG. 25. The temperature of the working fluid becomes lower, as a distance from the heating device 504 is longer.
Accordingly, the working fluid in the fluid container 502 consists of “gas-phase (steam) working fluid being vaporized” and “liquid-phase working fluid heated but not vaporized”, as a result of heating operation by the heating device 504. The liquid-phase working fluid, which moves toward the cooling device 506 together with the steam, is cooled down by the cooling device 506, without contributing in the fluid vibration (expansion and contraction of the working fluid). Therefore, the steam engine of this kind has a larger heat loss.